The present invention relates to a medical diagnostic method and apparatus for x-ray image presentation on a video monitor and, more particularly, to a method and apparatus for minimizing time delays between patient exposures due to camera film transport times.
In a typical imaging system used for medical diagnostics, primary imaging radiation, such as x-ray radiation which has been intensity modulated by passage through a patient, strikes an input screen of an image intensifier tube where it is converted to an electron laden image. Electrodes contained in the tube minify the image and accelerate the electrons toward a luminescent output screen of the image intensifier tube. An image having increased brightness is produced on the output screen in accordance with the spatial modulation of the x-ray radiation. A television camera and monitor are typically used to display the image. In addition, a photographic camera or cine camera is also used to record images of diagnostic interest.
High image quality, as measured by image resolution, contrast, and x-ray photon noise, is very desireable in such applications of an imaging apparatus. Typically, an intensity control system is provided in conjunction with the image intensifier tube for assuring that the intensity of a displayed image achieves a level established by a system operator. The level of intensity may be varied as a function of a desired contrast in order to allow an operator to view both low and high contrast images. Assuming that a level of intensity for the light output of the image intensifier tube is established at a fixed level, the rate at which that level of intensity is achieved is a function of the intensity of radiation applied to the patient and thus, may vary the exposure time of the patient to such x-ray radiation. Because the exposure time may vary, the time for the intensity level to reach the desired value will vary from exposure to exposure. Exposure times normally run for fractions of a second, for example, less than 400 milliseconds. In order to increase the rate at which film images can be generated so that higher frame rates can be achieved and not be unduly limited to short exposure times, it is desireable to reduce the delay time associated with film transport in the camera. That is, the camera frame rate becomes a limiting factor in determining the highest exposure frame rate and that limit tends to be established by the time required between frames, or more particularly, the film transport time. However, such film transport times are normally fixed times determined by how much time is required to perform the mechanical functions associated with film transport. For example, shutter opening and closing, opening of the film supply magazine port and removal of the next film, and moving the exposed frame are mechanical functions which require finite processing times.
Accordingly, it is an object of the present invention to provide a method and apparatus for higher frame rates in a camera.
It is another object of the present invention to reduce the delay time between successive camera frame exposures.
It is a still further object of the present invention to provide a method and apparatus for anticipating an end of a medical x-ray exposure.